The present invention relates generally to a solar collector, and more particularly to that member of the solar collector which provides conversion of the incident energy of the sunbeam radiation, to internal energy (heat) in a transportable cooling liquid.
A solar collector is a device which converts the energy in solar radiation to useful heat. The solar collector is preferably constituted by a black surface which absorbs the radiation. The surface is cooled by transferring the deposited heat to a cooling medium, preferably a gas or a liquid, in practice usually water, and is transported away. The black surface facing the sun is often covered by a transparent glass or plastic sheet in order to reduce heat loss to the surroundings.
In order to restrict the loss to the surroundings even further, so as to maximize the deliverable, useful quantity of heat from the solar collector, it is important to maintain the temperature of the radiation-absorbing surface as low as possible, in practice at a temperature as close as possible to the temperature of the cooling medium. In the most common solar collector configuration, this is achieved by providing the radiation-absorbing sheet with liquid-filled pipes in good thermal contact with the sheet. Often the liquid is water with added frost preventer (glycol). The radiation-absorbing surface or sheet if often made of metal, usually aluminium, to obtain a good thermal conductivity, so as to conduct heat effectively to the liquid-filled pipes. A disadvantage of this construction is that the liquid will always be inside the pipes of the radiation-absorbing sheet. The temperature conditions may vary, so that the liquid may boil or freeze. The temperature variations may also lead to substantial pressure variations.
Another disadvantage is that materials having very good thermal conductivity, i.e. metals, must be used. It would be advantageous to be able to use other materials like e.g. temperature resistant plastics, with regard to both weight and costs. Plastic solar collectors have already been put to use, however only a very simple variant without a glass cover, and preferably for heating swimming pools. Plastic solar collectors of this type do not exhibit the characteristics which can be obtained by means of the present invention.